A conventional speed adjusting device for a drill press is shown in FIGS. 1 and 2 wherein a driving shaft (100) of a motor (10) has a first variable pulley mounted thereto which is composed of two first disks (14), and an output shaft (11) has a second variable pulley mounted thereto which is composed of two second disks (18), and a belt (16) rotatably reeves between the first variable pulley and the second variable pulley. Each of the first disks (14) and the second disks (18) has an inclined surface so that the belt (16) is movably between the two inclined surfaces of the two first disks (14) or second disks (18). That is to say, the effective diameter of belt (16) in the first variable pulley (14) and the second variable pulley (18) is adjustable. A cap (13) is threadedly mounted to the top of the driving shaft (100) so as to adjust the gap between the two first disks (14), and a spring (17) is mounted to the output shaft (11) so as to exert a force to the second disks (18). A drilling bit (12) is connected to the lower end of the output shaft (11) so as to drill an object. Because the cap (13) is connected to the driving shaft (100) which is located away from the user as shown in FIG. 2, so that when the user wants to operate the cap (13) to reduce or increase the gap between the two first disks (18), he/she has to leave his/her seat to operate the cap (13). If the gap between the first disks (14) are reduced, the effective diameter of the belt (16) in the first variable pulley is increased, and the effective diameter of the belt (16) in the second variable pulley (18) is then reduced, so that the speed of the output shaft (11) is increased. Whenever, the user wants to adjust the speed of the output shaft (11), he/she has to leave from his/her seat and the adjustment of the speed of the output shaft is rough.
The present invention intends to provide a speed adjusting device which has a control means to adjust a pressing device on the output shaft. The user simply operates the control means beside him/her to adjust the effective diameter of the belt in the variable pulley on the output shaft.
The present invention improves the shortcomings of the conventional speed adjusting device and the speed of the drill press can be adjusted steplessly.